Novel extracellular, extra-embryonic and intercellular γ-tubulin assemblies in mouse oocytes and preimplantation embryos

Abstract

{gamma}-tubulin is a core component of microtubule-organizing centers (MTOCs), which are traditionally known as intracellular. Here, we report previously unrecognized extracellular, intercellular, and extra-embryonic {gamma}-tubulin assemblies in mouse oocytes and preimplantation embryos in three distinct categories: the {gamma}-tubulin extracellular satellite ({gamma}-TES), {gamma}-tubulin intercellular bridge girdle ({gamma}-IBG), and {gamma}-tubulin nucleation center ({gamma}-TNC). {gamma}-TESs are punctate structures outside the plasma membrane of oocytes and pre-hatching embryos. {gamma}-IBGs are transient, ring-like structures that, together with F-actin, encircle nascent intercellular bridges, suggesting a previously unrecognized role for {gamma}-tubulin in early intercellular bridge formation. {gamma}-TNCs are large, dynamic extracellular assemblies that emerge after fertilization and undergo stage-specific spatial and morphological reorganization during cleavage and blastocyst development. Both {gamma}-TESs and {gamma}-TNCs disappear after embryo hatching. Furthermore, {gamma}-TNCs and {gamma}-IBGs may represent large and ring-like aggregates of {gamma}-TESs, respectively, suggesting that {gamma}-TESs may serve as a local {gamma}-tubulin reservoir for higher order formations. {gamma}-IBGs and {gamma}-TNCs also exhibit close spatial association with microtubules, which form a peri-embryonic web lining the edge of the embryo exterior from zygotes to morulae. Together, our findings reveal a non-canonical, extra-embryonic {gamma}-tubulin organization system that may coordinate an embryonic skeleton architecture across blastomeres for critical embryo-wide developmental events such as polyspermy prevention, polarity establishment, morula and blastocyst formation, and embryo hatching.